Improving ozone resistance of butyl rubbers



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when, tlifey are used in United States Patentnwrnovnvo ozo E' RESISTANCEF BUTYL RUBBERS Augustus B. Small, Westfield, Leon Sherwood Minckler,Jr., Metuchen, John L. Ernst, Westfield, and, Francis P. Ford, Watchung,N.J., assignors to Esso Research and Engineering Company, a corporation,of Delaware No Drawing. Filed July 9, 1958, Ser. No. 747,336

'14 Claims. (Cl. 260-455) The present invention relates to an improvedozone resistant rubber and, more particularly, to a process forimproving ozone resistance by the addition of dimers of cyclic dienehydrocarbons to unsaturated rubbery polymers.

In the past, there has been a considerable problem concerning the effectthat ozone. has upon natural or synthetic rubbers. Deterioration ofrubbers, which unavoidably have unsaturation, is caused chiefly by theaction of ozone; cals which attack the double bonds that are present inthe rubber chain. Ozone is present in the atmosphere in very smallproportions, usually from 1 to 2 parts in 100,000,000 parts of air; butin certain localities the concentration is as high as 92 parts in100,000,000 parts ofair. Even this relatively low concentration of ozonein the air causes rubber to. crack, particularly when it is undertension, e.g., in tire casings, rubbertbands stretched around papers,and rubber tubing put" over laboratory stopcocks. Ozone is also formedwhen an electric spark occurs in an atmosphere of oxygen, e.g., theignition system of an automobile. This phenomenon is called coronadischarge and causes cracking of rubber whic may be in contact with theozone produced.

There are several methodsrpresently employed to increase the ozoneresistance of rubbers. The first method is to add wax to the rubberycompound. Since wax is.

Normally, ozone breaks down to form free 'radinot soluble in rubber, itwill tend to egress to the. surface of the material. Therefore, aphysical barrier is formed against the ozone. However, this procedurehas definite disadvantages; wax willwear off and, although more wax willcome to the surface, there may be a period of time when the rubber isexposed to ozone. It should also be.

noted that, if the rubber is stretched, the wax coating will crack andthe ozone will come in contact with the rubber.

Another method used for increasing the ozone resistance is to addcertain types of organic compounds to the rubbery material. Thesecompounds, which are known as anti-ozidants, react with thefreeradicalwhich results from ozone. Therefore, fewer double bonds are attacked bythese free radicals and deterioration of the rubber is decreased. Theanti-ozidants are generally either secondary aromatic amines orsecondary aromatic .phenols. Examples of the. aromatic amines arediphenyl amine; N.N-diphenyl-p phenylenediamine; and di-pmethoxydiphenylamine. However, the addition of these amines to the rubberhas falserious disadvantage, for rubber with these anti-ozidantadditiveswill stain and discolor items it comes in contact with,.e.g., weatherseals for automobile Windows, containing these, anti-ozidants,fwillstain the paintedsurface of the vehicle. N in addition tofthe amines,secondary aromatie phenols havefbeen used as anti-ozidants.Such'phenolsinclude:

hydroquinone monobenzyl ether and 4-methyl-6-tertebutyl However, thesephenols are acid materials and it t e conjunction withjrubber, a {cor--2,981,714 Patented Apr. 25, 1961 ice ozone resistance of unsaturatedrubbery polymers can be increased by the addition of dimers of cyclicdiene hydrocarbons, e.g., dicyclopentadiene. This method overcomes thedisadvantages previously encountered in the utilizatino of waxes andsecondary aromatic amines and phenols.

One embodiment of this invention is to'add diCYClO? pentadiene to therubbery polymer before and/or after curing. For example, the rubber,after it has been pre pared, can be compounded with dicyclopentadieneand other materials and cured as desired. However, the prepared rubbercan'also be compounded with materials, including or excludingdicyclopentadiene, and then cured by various methods The cured rubbercan then be immersed in dicyclopentadiene and dried by any known means.

The rubbery compounds to whichthis invention is applicable are anyunsaturated rubber such as butyl rubber, natural rubber, neoprene, SBR(the copolymer of major amounts of butadiene and minor amounts ofstyrene) and ABR (the copolymer of butadiene and acrylonitrile). Butylrubber is preferred. It has excellent ozone resistance initially becauseof the low unsaturation which it possesses (iodine number less than 50,generally about- 1 to 10). However, through the utilization of thisinvention, it is possible to increase the ozone resistance in butylrubber to an even greater extent.

a The butyl rubber polymer is prepared by reacting 70 to 995 parts byWeight, preferably'SS to 99.5 of an isooletin with 30 to 0.5 parts byweight, preferably 15 to 0.5, of multiolefin. The isoolefin, in general,is a C to C compound, e.g., isobutylene or'2-methyl-1-butene. Themultiolefi n, in generah is a C to C conjugated diolefin, e.g isopreue,butadiene, or piperylene. The preferred polymer is obtained by reacting95.to 99.5% by weight of isobutylene with 0.5 to 5% by weight ofisoprene.

Mixture of monomers, preferably with 1 to 5 volumes of inert diluent,e.g., methyl chloride, should be cooled to a temperature'between 0 and-200 C. and it is preferredthat the temperature range be between --60and C. The cold mixture is polymerized by the addition of'aFriedel-Crafts catalyst, preferably an alumi num halide catalyst in aliquid ordissolved form, inconjunction with vigorous agitation. Theamount of catalyst is generally about 0.15 to 1.0% by Weight of themixed olefins.

The polymerization reaction is rapid and the polymer precipitates out ofthe solution in the form of a slurry or flocculent white solid. Thepolymer, which is re covered and dried, has a Staudinger molecularweight between 20,000 and 150,000, preferably 45,000 to 60,000; and aniodine number between 0.5 and 50, preferably between 1 and 15. Thepreparation of this copolymer is described in US. 'PatentNor 2,356,.128.

The butylrubber, similarly to other rubbers, can be compounded withvarious other materials. Some example of the types of materials that canbe incorporated a 1 are as follows; stabilizers, plasticizers, fillers,accelerators,

worked on an open-roll mill with the addition of other compoundingingredients The butyl rubber within the scope of. this inventionincludes those which are-halogenated, eg chlorinated and brominated; thepreferred range of halogen the rubber structure is from 0.9 to 1.5;weight percent for chlorinated butyl rubber and 1.5

. The addition of dicyclopentadieue to neoprene has also been effectivein increasing its ozone resistance. Neoprene is prepared by polymerizingchloroprene by any a is added to the alkaline latex just beforecoagulation.

Coagulation is accomplished by freezing the surface of a large rotatingBryan-cured drum partially immersed in the latex. The resulting film isstripped from the freeze roll, thoroughly washed with water, squeezed,'and'dried. The resulting material is flexible, free'from odor, lightamber in color, and has a specific gravity of 1.23.

The dimers of the cyclic diene hydrocarbons within the purview of thisinvention, which increase the ozone resistance of rubber, arehydrocarbon ,dimers of cyclic diolefins as" dicyclopentadieue anddimethylcyclopentadiene. However, dicyclopentadiene is preferred. It iscritical for the success of this invention to use the dimer of thecompound, e.g., dicyclopentadieue. Under normal conditions the boilingpoint of the monomer is too low and furthermore, the monomer may revertto the dimer. However, the dimer will not polymerize with itself or therubber. Therefore, the dimer, e.g., dicyclopentadieue, is

' included in the rubber only as an additive and not as a reactant.- Inother words, the dimer is only compounded with the rubber and notreacted with it. I Dic'yclopentadiene can be prepared by any knownmeans. One method is by cracking petroleum fractions such as kerosene,gas oil, naphtha, etc., in the presence of steam at temperatures about1000 F. up to 1500 F. to give an unsaturated product stream. The liquidcut boiling between 80 and 350 F. is segregated and subjected to heatsoaking atabout 220 to 240 F. for 6 to 16 hours to dirnerize the cyclicdiolefins contained therein followed by separation of thedicyclopentadieue.

In accordance with this invention, the dicyclopentadiene maybe added tothe rubber in any one of three methods or in any combination of thesethree methods. The first method is to add the dicyclopentadieue as acompounding agent before the curing operation. This compound may beadded to the polymer by Banbury mixing and/or mill mixing. The amount ofdicyclopentadiene added is critical and should be in the range from 2 to20 parts per 100 parts of rubber. Below 2%, no antiozidant action isfound; above 20%, excessive plasticizing of the rubber is elfected. Thismethod will greatly improve the ozone resistance but will cause adecrease in the-physical propertiesor" the vulcanizate. That is, thevalue of the tensile strength, modulus, and elongation will decrease.'This reduction can be largely overcome by selecting the proper curingsystem.

A second method for the addition of dicyclopentadiene is after'thecuring step. In this method, the cured rubber is immersed indicyclopentadieue or an aqueous emulsion thereof. After a period of timethe vulcanizate swells, which indicates that the dicyclopentadiene hasbeen absorbed in the rubber. After immersion, the rubber is allowed todry and contract to its former shape. The immersing solution heretoforedescribed may contain 5.to'l00% dicyclopentadieue and 95 to water. Thetime will generally fall within the range of 1 minute to 3hours,depending on temperature and pressure. A temperature below 170 C. may beused,but room temperature is satisfactory. Pressure above atmosphere may350 FJfOr abouf'l to 16 hours. This after-cure method One suitablemethod is described hereincreases the ozone resistance of rubber andthere is bet-- ter retention in the physical properties. That is, theten sile strength, modulus, and elasticity are not decreasedas much aswhen dicyclopentadieue is compounded with: the rubber prior to curing.

The dicyclopentadieue can also be added by a third method which issomewhat similar to the first method described above. However, in thismethod the dicyclopentadieue is added before curing to preferred curesystems. This method will also increase the ozone resistance but willalso retain the physical properties, e.g., tensile strength, modulus,and elongation. Some of the preferred cure systems are below:

PARAQUIN/ONE- DIOXIME CURE Paraquinone dioxime in conjunction with leadoxide isan effective curing agent. vulcanization of the polymer appearto comprise the formation of aromatic nitroso groups which in turn reactwith the unsaturated units in the polymer chain, e.g., isoprene. Somesulfur may be added to improve product quality and aging resistance. Thepreferred parts per 100 parts of rubbery polymer are as follows: 1.0 to8.0 parts paraquinone dioxime, 5.0 to 20 parts lead oxide, and 0 to 4.0.partssulfur. Other materials may be added which include fillers, e.g.,carbon black; accelerators, e.g., zinc oxide; and'softeners, e.g., zincstearate.

PARAQUINONE DIOXIME DIBENZOATE CURE black; accelerators, e.g., zincoxide; and softeners; e.g.,

zinc stearate.

BEN ZOTHIAZYL DISULFIDE CURE Benzothiazyl disulfide acts as a mildoxidizing agent for paraquinone dioxime because of the cleavage of thee.g., stearic acid. The amount of dicyclopentadieue added disulfide toform two mercaptan molecules. Apparently, V

the conversion of the dioxime t0 the nitroso group brought about by theloss of a hydrogen atom results in the same type of vulcanizationmechanism as for the paraquinone dioxime cure, but the reaction is notas rapid. Sulfurmay be added only to improve aging resistance. Gthermaterials may be added but the preferred parts of constituents are asfollows: per parts of polymer, 1.0 to 8.0 parts paraquinone dioxime and0.5 to 4.0 parts sulfur,

ZINC OXIDE CURE In halogenated butyl rubber, zinc oxide is a suitable.

cure. Apparently there isa carbon-carbon-linkage in the rubber formed bythe removal of halogen atoms or by reaction of halogen atoms with zinc.Ultra accelerators, e.g., tetramethyl thiuram disulfide, can also beused in conjunction with the zinc oxide anda faster cure can be providedin the presenceof the halogen, atoms.

The preferred parts per 100 parts ofrubbery polymer are as follows: 3 to10 parts zinc oxide and 0 to 5 parts tetramethyl thiuram disulfiderOther materials may be added which include fillers, e.g., carbon black;softeners,

to this third method for any of the above cure systems will be intherangeof 2 to 20 partsper 100 parts of rubber. V

The rubber, e.g.' fore or after the addition of dicyclopentadieue. Anymethod can be employed as steam, pressure, or mold curing.Aparticularly.satisfactdrymethod is. to cure the rubbery polymer inmolds at a temperature rangingfrom 100 C.

The chemical reactions in thev butyl rubber can be cured either be I 1Compounds: i

ass sts to 200 C. for a time interval to -5 hours.

Thus,in accordance with this invention, a product can be prepared whichhas increased ,ozone resistance and overcomes the disadvantages ofprevious methods. For example, the product will not wear-off or crack asis the case with the wax'additive. Also, the product v.of thisinven tionwill not stain other items, which is a disadvantage for the use ofsecondary aromatic amines. Corrosion will not occur, thus overcoming thedisadvantage of secondary aromatic phenols. It :is possible through theuse of this invention not only to increase the ozone ,resistance butalso retain important physical properties, e.g., tensile strength,modulus, and elasticity.

The following examples are submitted to illustrate but not to limit-thisinvention.

ranging from 5 minutes Example I .Atub e y sepe mer contai ing 985%isobuty ne and 1.5% isoprene was chlorinated to produce a productcontaining 12 c ori e i its s uc u Ru ber A wa obtained by adding thefollowing compounds;

Compounds: V 'Parts Chlorinated copolymer 100 Dicyclopentadiene 4 MPCblack 50 Stearic acid V 1 Zinc oxide V 5 Amberol ST 137 14 a Carbonblack.

Alkali catalyst reaction product of 1 mol 4-octyl phenol and 2 molformaldehyde. The above compounding was accomplished by subjecting thechlorinated copolymer to a mill mixing. All compounding ingredients wereadded while keeping the mill rolls cool (75 F Thecompounded polymer wasthen cured in molds at a temperature of 307 f F. for 60 minutes.

The characteristics of Rubber A were compared to Control A which was thesame as Rubber A without the dicyclopentadiene additive:

It is the addition .of dicyclopentadiene results in a compounded rubberwhich is able rto2withstandan exposure of 0.2% ozone for. longer than .6.hours.

i Example II" 5 d The abo comp u n an u i g e e c omplished by a similarprocedure described in Example I. l

The characteristics of this Rubber B were compared to Control B whichwas the same as Rubber B without No cracks were produced when thedicyclopentadiene was added to the rubber. Physical properties wereretained as a result of this care system.

A rubliefv r y ner conta nin 98-5 s. i. ylene and 1.5 isoprene waschlorinatedto produce a product containing 1.2% chlorine in itsstructurel Rubber B was obtained by adding the following, compounds:

1 I LParts Chlorinated copolymer an.

The chlorinated rubber was able to withstand a longer Carbon black.

Example III A rubbery copolyrner containing 98.5% isobutylene and 1.5%isoprene was chlorinated to produce a product containing 1.2% chlorinein its structure. Rubber C was obtained by adding the followingcompounds:

Compounds: Parts Ch r t po y 00 SRF black 50 Dicyclopentadiene 4 Stearicacid l Zinc oxide i v 5 Antioxidant .2246 a 1 'Iuads 1 iitlifiti yith55.2%.?iluiriifiialiil The above compounding andcuring wereaccomplished by a similar procedure described in Example I.

The characteristics of this Rubber C were compared to Control C whichwas'the same as Rubber C without the dicyclopentadiene additive.

Tensile Modulus Elongm strength, at 800% tion,

.p.s.i. elongation, percent p. s.i.

RubberC 2,120 1,150 500 ControlC 1,900 1,250 480 9.2 O: EXPOSURE Minutesto- Alter Oatest Total time Crack Break hrs. Tensile Mod- Elonga-.strength ulus tion Rubber 315 346 Control o 137 exposure to ozone as aresult of the addition'of dicyclopentadiene. The physical properties ofthe rubber with) or withoutdieyclopentadiene were about thesame.

' Example 1V new. op me collat n 9 5% and-1.5% isgprene washrominated'to re M eesmri containing 2.1% bromine in its structure.Rubber D is obtained by adding the following compounds:

to 0.2% ozone for 6 hours. Physical properties were'retained through theutilization of this cure system. p

Compoundm' i v ExizrinpleiVl I Brommated copolymer; 100 r I I 1 R1?black 50 O A rubbery copolymer containing 98.5% rsobutylene and st riacid 1 1.5% isoprene was compounded as follows'to provide 'Zinc oxideRubbers A, B, C, D, and E.

- -Dicyclopentadiene 4 V i p V The above compounding and curing wereaccomplished oompmmd A B O D E by a similar procedure described inExample I. Co 01 m0 The characteristics of Rubber D'were compared to ggfiii' igljjfjf"""jjjjjj :1: 51 Control D which was the same as Rubber Dwithout the dicyclopentadiene additive. i e5 7 5 r 1 2 4 Tuads 2.4 1.2-2.4 2.4 Tensile Modulus Elongastrength, at 300% tion,

p.s.i. elongaiidon, percent a Carbon black (MOP).

1 r r H V V p 7 The compound and curing were accomphshed by a 81m].-Rubbern 2,090 910 490 20 lar procedure described in Example I. ControlD5 2,110 1, 250 490' The characteristics of these compounded and curedrubbers were compared. 0.2% 03 EXPOSURE A B 0 D E Minutes to v After 0test Total time .ie .123 2 Crack Break hrs. Tensile Mod- Elon a- ,615 2,55 strength ulus tier? 575 60 '1, 050 '82 645 Rubber-D 6 2,100 740 5200.2% 03 EXPOSURE ControlD 251 269 3O V p A B C D E The addition-ofdicyclopentadiene has produced a rubber i V V which was able towithstand an exposure to 0.2% ozone Minutes to eraok 22 as 1,200 392 160for 6 hours without cracking or breaking. The tensile f w 31 45 1,200

strength of the rubber was about the same as thecontrol.

. Example V 1 p A rubbery copolymer containing 98.5 isobutylene and 1.5%isoprene was brominated'to result in a product containing'2.1% brominein its structure. Rubber E was obtained by adding the 'followingcompounds:

Compounds: Parts -.Brominated copolymer 100 SRF. black 50' Stearic acid1 Zinc oxide 1 Antioxidant 2246 l Tuads 1 Dicyclopentadiene 4 The abovecompounding and curing were accomplished by a similar proceduredescribed in Example I..

The characteristics of Rubber- E were compared to control E which wasthe same as Rubber E without the dicyclopentadiene additive. v

compounded iviith fdicyclopentadiene which was exposed i The above dataindicate that dicyclopentadiene increases ozoneresistance.

Example VII A rubbery copolymer containing 98.5% isobutylene and 1.5isoprene was compounded to produce Rubbers H, I, J, K, and L. Rubber Hwas formulated as follows:

Compounds: P t (iopolymer MPC black 50 Zinc'oxide 5 PBN 0.2 Zincstearate 1 Sulfur V l Tuads 1.2 Dicyclopentadiene 2 Rubber 1 wasformulated as follows: Compoundsz- 1.. Parts Copolymer I 100 MPC black 750 Zinc oxide 5 'Stearic acid 1' -if DOTGe 1.5

" L-Sirlfur 2 Tuads b i 1.5 Dicyclopentadiene 2 vgDiorthptolylguanidirie. accelerator. V I V Rubber J was-formulated asfollows: I

Compounds: 4 Parts V Qopolymer .100; j ;M. Q...b, a. H V. v. I 50 3 Zncupzddev 3;. j H I i 5 lix qjstsar iq, r Su f Rubber K was formulatedas follows:

Compounds: j Pitfl Copolymer 100 MPC black V 9. Zinc oxide i i 5 Zincstearate i .0 1 Lead oxide I 5 Sulfur i 0.. J Tuads i .0 L5Dicyclopentadiene 5 Rubber L was formulated as follows:

Compounds: Parts Copolymer 100 MPC black 50 Zinc oxide 5 Stearic acid v1 DOTG Sulfur i 2- Tuads A -5 Dicyclopentadiene v V V t I Banbury mixingwas used to incorporate MPC black, zinc oxide, PBN, and zinc stearate.Other ingredients added on cold mill (75 F.). The compounded rubber wasthen cured in a mold at 307 F. for 60 minutes. i

The characteristics of Rubbers H, I, J, K, and L are compared to ControlH which was the same as Rubber H without the dicyclopentadiene additive.

Tensile Modulus Elongastrength, at 300% tion,

p.s,i. elongation, percent ps1.

Rubber H 3, 200 35 720 Rubber 1.. 1, 910 150 1, 035 Rubber .T 2, 060 220065 Rubber K- 2, 240 270 875 Rubber L. 1, 070 100 1, 235 Control H 2,925 1, 015 t 570 0.2% O: EXPOSURE Minutes to- After 0 test Total time Ii Crack Break hrs. Tensile Modu- Elongastrength lus tion Rubber H 122133 Rubber I r. 6 970 100 1, 040 Rubber J 6 2, 150 225 i 970 Rubber K- 62,190 290 790 Rubber L- 6 Unknown 70 {1,300 Control H. i

A rubbery copolymer containing98.5% isobutylene and 1.5% isoprene was"compounded to pgoduce Rubber Compounds:

Copolymer' MPC black Zinc oxide Zinc stearate Red-lead i i Dibenzo GMFQ. 'Sulfur Q f1; Dicyclopentadiehe "our: Pboi V bParagntxionedioxlmebenzoat e., h

Parts Control M which was the same as Rubber M wiihout 1:0 Banburymixing was used to incorporate MPC black, zinc oxide, PBN, and zincs'tearate." Other ingredients added on cold mill (75 F.). The compoundedrubber was then cured in .a mold at 307 F. for 60 minutes. i

The characteristics of Rubber M were compared to the dicyclopentadieneadditive.

The addition of dicyclopentadiene has produced a compound rubber whichwas able to withstand an exposure of 0.2% ozonei for 6 hours withoutcracking and withp out breaking; The physical properties were alsoretained Tensile Modulus Elongastrength, at 300% tion;

p.s,i. elongation, percent i M p.s.i.

, "RubberN 515 1,300 GontrolN.. 3, 35 680 720' ambinxrosunn Minutes tolAttends test Total i Home Crack Break hrs. Tensile 'Mod- Elongastrengthulus 7 tion n bbermxi. ."48' 375 75, 1,125- a Control N- 20 -20 with theutilizationiof this ure system.

Example IX A rubbery copoly mer containing 98.5% isobutylene and 1.5%isoprene was compounded to produce Rubber N. Rubber was obtained asfollows:

Banbury was used to incorporate zinc oxide, PBN, and zinc stearate.Other ingredients added on cold mi1l;(75- F.). The compounded rubber wasthen cured in a mold at 307 F. for 60 minutes. a a i The characteristicsof Rubber N were compared to Control N which was theisame asdicyclopentadiene additive.

the rubbery compound; a 7

Rubber N withoutthe 1 1 Example X 'A' rubbery copolymer :containing.985% isobutylene and 1.5% isoprene was compounded as follows:

. Compound: Parts Copolymer a 100 FEF black 30 SRF black 80 Zinc oxidePetrolatum Sulfasan R b 1.25 Spider sulfur 1.25 TMTDS 1.5 'MBT e p 2.

I Carbon black (furnace black). 'Morpholine disulfide, nonbloomingsulfur donor. c Fine particle size, better dispersion of sulfur.

V Tetramethyl thiuram disulfide, accelerator.

7 Mercapto benzo thiazole ("Captax). The following additional materialswere compounded with the above to produce Rubbers 0, P, Q, R, S, T, U,and V.

Rubber Compounds Parts 0 Dieyclopentadieue 1 P fin {i} a 1 T- o V 3 9'..80% butadlene-20% styrene polymeric oil H :1,

o i v Banbury mixing was used to incorporated carbon black, zinc oxide,MBT, and zinc stearate. Other ingredients added on cold mill (75 F.),The compounded rubber was then cured in a mold at 307 F for 60 minutes.

In the following table, the characteristics of Rubbers O, P, Q, R, S, T,U, and V are compared to Control R which is the same as all of therubbers without the dicyclopentadiene, dimethylcyclopentadieue, maleicanhydride, or butadiene-styrene polymeric oil additives.

'lhe aboyedata show thatoaone resistance is increased by the addition ofabove- 1 part of dicyclopentadiene or dimethyl cyclopentadiene', but isdecreased by the addi- V Example XI rubbery copolymer'containing 98. 5%isobutylene V and 1.5% isoprene was compounded to produce Rub ber W.Rubber W was obtained as follows:

Banbury' mixingwas used to iuc'orporateiMilC iblack; zinc oxide; PBN,and zinc stearate. Other ingredients added on cold mill (75 F.). Thecompounded rubber was then cured in a mold at 307513. for 60 minutes.

- Aft'efRubber W was cured, it was immersed into a solution containing100% dicyclopentadiene for 3 hours. At the end of this'time, the rubberabsorbed dicyclopentadiene to produce a swollen rubber with 10%dicycloperitadiene in its'structure. Room temperature and atmosphericressure were employed in this process.

ii The immersed rubber was dried by exposure to air at room" temperature'for 16 hours The characteristics of Rubber W were compared to Control Wwhich was the same as Rubber W without the immersion indicyclopentadiene.

N 'I ensile Modulus Elongastrength; at 300% tion,

p.s.i. elongation, percent M psi.

Rubber w '2,5s0 590 680 Control W-.. 3.350 060 690 0 2% 0: EXPOSUREMinutes to After 03 test e Total time Crack Break hrs. Tensile ModElongastrength ulus tion Rubber a 2.340 590 650' ControlW The ozoneresistance of the rubber'is increased by i'm mersing it after curing ina solution of dicyclopentadiene.

' tion of maleic anhydrideor .butadiene-styrene polymeric. M d

compounds: 7 Parts Copolymer MPC black 7 V 50 ZlHCiOXldC 5m;

.PBN 0.2- Zinc'stearate 1 Sulfur Y 1 2. il ft 5%:

Example XII A rubbery copolymer (neoprene) containing 100% chloroprenewas compounded with 5 parts of dicyclopentadiene per 100 parts of thepolymer. The compounding was performed as in Example I. The compoundedpolymer was then cured in molds at a temperature of 307 F. for variousperiodsof time.

Characteristics of this compounded rubber were compared to a controlwithout the dicyclopentadiene addi-" tive.

' V nns uij'rs FOR io-MrNu'rn 6mm Conipounded Control rubber Tensilestrength 3. 3, 370- Modulus 2, 070 2, 820 Elongation 480 405 Minutes tobreak after exposure to 0. 1 1'. 5 8

RESULTS FOR 20-MINUTE CURING Compounded Control '1 rubber j Tensilestrength 2, 880 3, 610 o ulus 2, 150 2, 920 Elongation 415 400 Minutesto break atter. exposure to 0.2% 03.. 11 7. 25

a nsufis' r'on "ioMlNurn ounueo Q Compounded Control h rubbet Tefisilestrengti 2', i a, 590 Modulustz'nzzr 2,590 3, 450 Elnnnntjnn v v V 7410'1 325 v utes to break after exposure to 0.2% 03.... 13. 5 7. 75

Th a epteri eyee aanee toinor rcn l r h 9i .ernq nreto name be re bre aoccurred- Therefore, neoprene with dicyclopentadiene has increased 1 Theabove examples ljthe addition of dimers of cyclic diene hydrocarbons,e.g., dicyclopentadiene and dimethylcyclopentadiene, to unsaturatedrubbery polymers, e.g., butyl rubber and neoprene, improves the ozoneresistance of the polymers. It is critical to employ between 2 and 20%of the dimer in the rubber. However, the cyclic diene dimer can beincorporated in the rubber before and/or after it is cured.

Having described the general nature and specific embodiments of thepresent invention, the true scope is now particularly pointed out in theappended claims.

What is claimed is:

1. A vulcanizate which comprises 100 parts of an unvulcanized rubberypolymer selected from the group consisting of butyl rubber copolymer ofmajor C to C isoolefin with minor C to C diolefin, halogenated butylrubber copolymer of major C to C isoolefin with minor C to C diolefin,and polychloroprene, which has been compounded with 2 to 20 parts of adimer of a cyclic diene hydrocarbon selected from the group consistingof dicyclopentadiene and dimethylcyclopentadiene and subsequently curedat a temperature between 100 and 200 C. for 5 minutes to 5 hours toprovide said vulcanizate therefrom with increased ozone resistance.

2. The vulcanizate according to claim 1 in which the curing is performedin the presence of a compound selected from the group consisting ofparaquinone dioxime, paraquinone dioxime dibenzoate, and zinc oxide.

3. The vulcanizate according to claim 1 in which the rubbery polymer isa butyl rubber copolymer of a major C to C isoolefin with minor C to Cdiolefin.

4. The vulcanizate according to claim 1 in which the rubbery polymer isa halogenated butyl rubber copolymer of major C to C isoolefin withminor C to C diolefin.

5. The vulcanizate according to claim 1 in which the rubbery polymer ispolychloroprene.

6. A vulcanizate which comprises 100 parts of an unvulcanized rubberycopolymer of 70 to 99 parts by weight isobutylene with 30 to 0.5 partsby weight of isoprene which has been compounded with 2 to 20 parts ofdicyclopentadiene and subsequently cured at a temperature between 100and 200 F. for 5 minutes to 5 hours to provide said vulcanizatetherefrom with increased ozone resistance.

7. A vulcanizate which comprises 100 parts of an unvulcanized rubberycopolymer of 70 to 99 parts by weight isobutylene with 30 to 0.5 partsby weight of isopreue which has been compounded with 2 to 20 parts ofdimethylcyclopentadiene and subsequently cured at a temperature between100 and 200 F. for 5 minutes to 5 hours to provide said vulcanizatetherefrom with increased ozone resistance.

8. A process which comprises compounding 100 parts of an unvulcanizedrubbery polymer selected from the group consisting of butyl rubbercopolymer of major C to C isoolefin with minor C to C diolefin,halogenated butyl rubber copolymer of major C to C isoolefin with minorC to C diolefin, and polychloroprene, with 2 to 20 parts of a dimer of acyclic diene hydrocarbon selected from the group consisting ofdicyclopentadiene and dimethylcyclopentadiene; and subsequently curingat a temperature between 100 and 200 C. for 5 minutes to 5 hours toprovide a vulcanizate there from with increased ozone resistance.

9. The process according to claim 8 in which the curing is conducted inthe presence of a compound selected from the group consisting ofparaquinone dioxime, paraquinone dioxime dibenzoate, and zinc oxide.

10. The process according to claim 8 in which the rubbery polymer is abutyl rubber copolymer of major C to C isoolefin with minor C to Cdiolefin.

11. The process according to claim 8 in which the rubbery polymer is ahalogenated butyl rubber copolymer of major C to C isoolefin with minorC to C diolefin.

12. The process according to claim 8 in which the rubbery polymer ispolychloroprene.

13. A process which comprises compounding 100 parts of an unvulcanizedrubbery copolymer of to 99.5 parts of isobutylene with .5 to 30 parts ofisoprene with 2 to 20 parts of dicyclopentadiene; and subsequentlycuring at a temperature between and 200 C. for 5 minutes to 5 hours toprovide a vulcanizate therefrom with increased ozone resistance.

14. A process which comprises compounding 100 parts of an unvulcanizedrubbery copolymer of 70 to 99.5 parts of isobutyleuewith .5 to 30 partsof isoprene with 2 to 20 parts of dimethylcyclopentadiene; andsubsequently curing at a temperature between 100 and 200 C. for 5minutes to 5 hours to provide a vulcanizate therefrom with increasedozone resistance.

References Cited in the file of this patent Le Beau, Rubber Age, Vol.68, No. 1, October 1950, pages 49-56.

Taft et al.: Rubber Age, vol. 75, No. 6, September 1954, pages 838-840.

1. A VULCANIZATE WHICH COMPRISES 100 PARTS OF AN UNVULCANIZED RUBBERYPOLYMER SELECTED FROM THE GROUP CONSISTING OF BUTYL RUBBER COPOLYMER OFMAJOR C4 TO C7 ISOOLEFIN WITH MINOR C4 TO C10 DIOLEFIN, HALOGENATEDBUTYL RUBBER COPOLYMER OF MAJOR C4 TO C7 ISOOLEFIN WITH MINOR C4 TO C10DIOLEFIN, AND POLYCHLOROPRENE, WHICH HAS BEEN COMPOUNDED WITH 2 TO 20PARTS OF A DIMER OF A CYCLIC DIENE HYDROCARBON SELECTED FROM THE GROUPCONSISTING OF DICYCLOPENTADIENE AND DIMETHYLCYCLOPENTADIENE ANDSUBSEQUENTLY CURED AT A TEMPERATURE BETWEEN 100 AND 200O C. FOR 5MINUTES TO 5 HOURS TO PROVIDE SAID VULCANIZATE THEREFROM WITH INCREASEDOZONE RESISTANCE.